[Nek5000-users] perturbing interior variables

Tue May 11 07:38:27 CDT 2010

Hi Frank,

One additional note.

It's important that your perturbed T() be continuous.

This could be done, e.g., via the following code in userchk

        if (istep.eq.0) then
           n=nx1*ny1*nz1*nelt
           do i=1,n
              t(i,1,1,1,1) = t(i,1,1,1,1) + perturbation of choice
           enddo
           call dsavg(t)
        endif

The dsavg() will ensure that T is continuous.   If T is not
continuous at the beginning, it will be discontinous forever
since we only solve for delta T and then add this to T.

Paul

On Tue, 11 May 2010, nek5000-users at lists.mcs.anl.gov wrote:

>
>
> Hi Frank,
>
> Boundary values will be set by userbc().
>
> There is no opportunity to intercede between userbc() being called
> and the solver.  (In effect, userbc() _is_ the opportunity to
> intercede.)
>
> userchk is called at the end of each step and therefore effectively
> at the beginning of the next.  Perturbing there will work - you can
> perturb all values and rest assured that values on Dirichlet surfaces
> will be overwritten by userbc.   Values on Neumann surfaces, however,
> would not be reset by userbc.
>
> hth,
>
> Paul
>
> On Tue, 11 May 2010, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Thanks for the replies, Aleks and Stefan.  I am still not clear on one
> point though.  Are changes made to temperature or velocity on boundaries
> in "userchk" at each time step irrelevant since they are overwritten by
> calls to "userbc"?
>
> Cheers,
> Frank
>
>
> On Mon, 2010-05-10 at 18:15 +0200, nek5000-users at lists.mcs.anl.gov
> wrote:
>> The heat solver calls BCDIRSC which will apply Dirichlet bcs. All 't  ' 
>> boundary points call userbc so you have the full control over the values at 
>> the boundary.
>> 
>> Stefan
>> 
>> 
>> 
>> 
>> On May 10, 2010, at 6:00 PM, nek5000-users at lists.mcs.anl.gov wrote:
>> 
>> > Hi Frank,
>> > > > I assume that you refer to t(i,j,k,iel) as temperature -- to be safe 
>> it should be t(i,j,k,iel,1)...
>> > > > In timestepping loop, subroutine userchk is called last by one -- 
>> right before the last one -- prepost which dumps field files .f or .fld -- 
>> see nek5_svn/trunk/nek/drive1.f:
>> > >      DO ISTEP=1,NSTEPS
>> >         call nek_advance
>> >         call userchk
>> >         call prepost (.false.,'his')
>> >         if (lastep .eq. 1) goto 1001B
>> >      ENDDO
>> > > while, as I can see, userbc for a passive scalar is called from a chain 
>> of subroutines nek_advance > heat > cdscal > BCNEUSC/BCDIRSC
>> > > This means that perturbation of temperature at the boundary won't be 
>> overwritten in userbc.
>> > > > One way to apply perturbation everywhere including the element faces 
>> that are not on the boundary of your domain is simply to multiply your 
>> perturbation factor by a function that goes to zero on the boundaries, 
>> e.g.:
>> > >   t(i,j,k,iel,1)=.99*t(i,j,k,iel,1)*(xm1(i,j,k,iel)**2.-1.)
>> > > in case the boundary surface plane is at x=1 & x=-1
>> > > Best,
>> > Aleks
>> > > > > > > > On Mon, 10 May 2010, nek5000-users at lists.mcs.anl.gov wrote:
>> > >> Hello all,
>> > > I am trying to perturb the temperature in a small part of the flow.
>> > However, I only wish to perturb in the interior and not on a boundary.
>> > I have the following in "userchk".  If I instead looped from "k=1,nz1"
>> > instead of "k=2,nz1-1", would this change the BC's?  The general
>> > question would be, does changing uvw & T in "userchk" change BC's or
>> > does "userbc" override what is done in "userchk"?
>> > > Cheers,
>> > Frank
>> > >        do 100 iel=1,nelv
>> >        do 100 k=2,nz1-1
>> >        do 100 j=2,ny1-1
>> >        do 100 i=2,nx1-1
>> >        if(((xm1(i,j,k,iel)-1.1)**2
>> >     &    + (ym1(i,j,k,iel)-1.1)**2
>> >     &    + (zm1(i,j,k,iel)-.45)**2)**.5.le..25)then
>> >           t(i,j,k,iel)=.99*t(i,j,k,iel)
>> >        endif
>> >          enddo !n
>> > 100     continue
>> > > > > > -- > Frank Herbert Muldoon, Ph.D. Mechanical Engineering
>> > Technische UniversitÃ¤t Wien (Technical University of Vienna)
>> > Inst. f. StrÃ¶mungsmechanik und WÃ¤rmeÃ¼bertragung (Institute of Fluid
>> > Mechanics and Heat Transfer)
>> > Resselgasse 3
>> > 1040 Wien
>> > Tel: +4315880132232
>> > Fax: +4315880132299 Cell:+436765203470
>> > fmuldoo (skype)
>> > 
>> http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html
>> > > _______________________________________________
>> > Nek5000-users mailing list
>> > Nek5000-users at lists.mcs.anl.gov
>> > 
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users_______________________________________________
>> > Nek5000-users mailing list
>> > Nek5000-users at lists.mcs.anl.gov
>> > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>> 
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> -- 
> Frank Herbert Muldoon, Ph.D. Mechanical Engineering
> Technische UniversitÃ¤t Wien (Technical University of Vienna)
> Inst. f. StrÃ¶mungsmechanik und WÃ¤rmeÃ¼bertragung (Institute of Fluid
> Mechanics and Heat Transfer)
> Resselgasse 3
> 1040 Wien
> Tel: +4315880132232
> Fax: +4315880132299 Cell:+436765203470
> fmuldoo (skype)
> http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users